The invention relates to a track by which a mining machine hauls itself in either direction along a mine face.
Several problems are experienced with existing tracks:
1. The conveyor pans to which the current tracks are attached, must articulate in the horizontal plane in order to advance the conveyor and in the vertical plane to allow the conveyor to accommodate undulations in the mine floor. Toothed rack tracks are known where this articulation effects the pitch between the teeth of adjacent racks to an extent where the error in pitch adversely affects the engagement between the driving means of the mining machine (e.g. wheel, pinion or continuous chain) and the racks.
2. Conversely the racks of some existing tracks maintain a gap at the same side of the conveyor pan to which they are attached and consequently reduce the amount of articulation available to the conveyor. In turn this restriction places on the racks the relatively high forces required to advance the conveyor over the mine floor; bearing in mind that this advancement can take place over say 10 adjacent pans each approximately 1.5 meters long compared to a width of 0.75 meters it can be seen that forces theoretically 20 times that which pushover rams can generate will be exerted on the joint between adjacent racks. To design a joint strong enough to withstand such forces requires a considerable amount of cross sectional area not normally available in the vicinity of the track (but normally available in the vicinity of the sides of the conveyor pans).
3. Other tracks are known in which a roller chain is captivated in furnishings attached to the face side of the conveyor pans or alternatively a round link chain is captivated to the spill plates attached to the goaf side ofthe conveyor pan and these tracks assist in overcoming the problems at 1. and 2. above. However, since the contact ratio between the driving means of the mining machine and track is rarely greater than 1 the profile of the roller chain or the round link chain where it engages with the driving means of the mining machine creates on the driving means, high tooth pressures and high separating forces relative to the haulage force.
4. During the cycle of one of the teeth (or rollers) of existing mining machine driving means engaging a tooth or link of existing tracks, travelling across it, and consequently leaving as the drive is taken up by the adjacent teeth, fluctuations in power are required to maintain the required haulage effort. These repeated fluctuations in power demand, created by the relative profiles of driving means and rack, subject the driving means, the drive reduction gearing and the associated prime mover (either hydraulic or electric motor) to high fluctuations in load, which can adversely affect the reliability of these elements.
5. Other tracks are known where, in order to accommodate articulation of the conveyor pans, alternate racks are allowed a limited amount of end float. This facility produces in the driving means, the reduction gearing and associated prime mover high shock loads each time the drive has to take up this end float in conditions where the pans are not articulated to one another.